(v) to engage in sexual intercourse with the intent, unbeknownst to the partner, of causing a pregnancy. This word is used specifically in instances where one partner believes that birth control is intact or being used, while the other has damaged/removed birth control without the knowledge or consent of the first partner, for an ulterior motive such as forcing the partner into a shotgun wedding situation as a means of securing the partner as a mate, or producing a child that the partner does not yet/ever want. This may include but is not limited to intentionally missing the Pill, removing diaphragms, or poking holes in a condom. Although more commonly done by women, men have also engaged in oopsing.
Oopsing involves an obscene abuse and betrayal of the partner's trust, not to mention the objectification of the partner into someone whose plans to remain childless, for whatever reason, no longer matter. Oopsing is thusly one of the most disgusting acts imaginable, and ought to be a prosecutable offence.

'How could you oops your lover? Shame on you for stooping to such betrayal!'

When you are having sex with a girl and,without her expecting it, you stick it in her ass. When she turns to look at you with that "What're you doing?" expression, you say "Oops!" and start railing her in even harder in the ass.